I. Field of the Invention
The present invention relates to an annealing apparatus for annealing only a portion of a tubular workpiece.
II. Description of Related Art
There are many circumstances in industry where it is desired to anneal a tubular workpiece. For example, when the tubular workpiece has been deformed into the desired shape, annealing the now deformed workpiece relieves not only stress and strain within the workpiece, but also prevents micro cracks which may be formed in the workpiece during the forming process. The annealing process, however, oftentimes disadvantageously weakens the workpiece.
Previously, in order to anneal metal workpieces, the metal workpieces are conventionally placed within an annealing furnace and heated to their annealing temperature. Simultaneously, in order to prevent discoloration of certain workpieces, for example stainless steel workpieces, the workpieces are kept within an oxygen-free nitrogen and/or hydrogen atmosphere.
A primary disadvantage of these previously known annealing furnaces is that such annealing furnaces are expensive to maintain and operate.
A still further disadvantage of these previously known annealing furnaces is that the annealing furnaces anneal the entire workpiece. However, since the entire workpiece is subjected to the annealing temperatures, rather than only the portion for which annealing is needed, the annealing process may unduly weaken the entire workpiece.
The present invention provides an apparatus for annealing a workpiece, such as an automotive fuel fill pipe, which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the apparatus of the present invention comprises an elongated tube which is dimensioned to receive the workpiece so that a first end of the workpiece as well as the portion of the workpiece to be annealed is positioned within the tube while a second end of the workpiece extends outwardly from the tube. Furthermore, only a portion of the workpiece has been deformed so that annealing of only that portion is desired.
An induction coil is disposed coaxially only around the portion of the workpiece for which annealing is desired and this induction coil is positioned outside the tube. Upon energization of the induction coil, the induction coil locally heats to annealing temperature only the portion of the workpiece for which annealing is desired.
The apparatus further includes a source of pressurized nitrogen and/or hydrogen which is fluidly connected by a conduit to the second end of the workpiece. Nitrogen/hydrogen thus flows from the source, and into the interior of the tube thus creating an oxygen-free environment within the tube prior to energization of the coil. This nitrogen continues to flow upwardly through the interior of the workpiece and downwardly along the exterior of the workpiece during energization of the coil. Ultimately, the nitrogen/hydrogen gas is exhausted out through the second end of the tube. In practice, this nitrogen/hydrogen flow through and around the workpiece during induction heating of the workpiece by the induction coil minimizes discoloration of the workpiece.